1. Field of the Invention
One aspect of the present invention relates to a method of coating a substrate for adhesive bonding.
2. Background Art
In producing many articles, often it is necessary to join dissimilar materials. In many cases, one or both of the materials must have their surface properties adjusted. Adjusting surface properties of materials in manufacturing often involve surface treatment technologies. Non-limiting examples of these surface properties include the surface energy, chemical inertness, conductivity, receiving dyes, and adhesion. Non-limiting examples of applications using surface treatment and preparation include anti-corrosion coatings on corrodible metals such as iron and steel; bio-compatible coatings on implants; waterproof layers on electronics; and adhesives on glass.
Applying coatings, adhesives, sealants, and elastomers (CASE) to substrates often require particular care in treating or pre-treating the surface to avoid adhesive failure between the substrate and the applied CASE compounds. Many CASE application processes involve steps of (a) cleaning or roughening the surface, (b) applying a primer that either bonds to the surface or etches it, and (c) applying an enhancement agent that adds additional bonding functionality. CASE compounds are used in industries including construction, automotive, medical, dental, labeling, electronics, and packaging.
In the automotive industry, CASE compounds are used in conjunction with glass glazing processes. Disadvantageously, automotive glazing glass is susceptible to breakage from mechanical shocks striking at its edges. As a consequence, the edges are typically encapsulated. In one encapsulation method, a frame connects the automotive glazing glass to the vehicular superstructure. The frame thereby borders portions of the glass. In one method for bonding the glass and frame components, the glazing glass is cleaned with a solvent, a primer containing a coupling agent to chemically modify the surface is applied to the surface, and finally, a thicker layer of a paint-like compound which bonds well to the frame is applied. In this example, properly aligning the two layers, i.e. primer and paint-like compound layers' present difficulties because the primer becomes effectively transparent on glass when dried and the second coating is opaque, prohibiting accurate alignment when the application width is wider than that of the primer coat.
When glazing glass is used as a windshield, it is intended to prevent mass and energy transfer into the passenger compartment, such as wind, rain, debris, and infrared heat, while contributing to passenger safety by increasing structural integrity during vehicle crash and rollover scenarios. In some instances, the glazing glass is not a homogeneous surface as it may have frits in some area to shade from infrared, ultraviolet and other wavelengths of light. Likewise, it may have areas that are tinted. Further, it may have gaps in these features to permit application of fasteners. These gaps may need labor-intensive masking during application of a second layer of sealant.
Other aspects of joining dissimilar materials include desires to improve accuracy of manufacturing, productivity, levels of automation, reliability, and/or manufacturability while decreasing harmful side effects, quantity of materials used, and/or waste of energy and materials. For example, some CASE compounds have substantial amounts of waste. Often coupling agent primers are less than 1% active agent and 99% carrier solvent. In another example, cleaning materials have harmful side affects such as flammability and/or noxious solvents like isopropyl alcohol or toluene. In other cases, paint-like layers often have to air dry within 30 seconds and so use volatile solvents. Energy and money are wasted to remediate these emissions and to protect workers' health.
Recently, plasma polymerization has been developed as a tool to modify material surfaces while improving manufacturability, levels of automation, and accuracy of manufacturing, while decreasing harmful side effects as well as waste of energy and materials.
There are different types of plasmas that are defined by their output temperature, their pressure conditions, as well as the equilibration state regarding the chemistry and thermal state. For example, there are plasmas created under subambient pressure conditions. Examples include a high plasma density mode and a low plasma density mode plasma generated with a magnetron which is typically used in physical vapor deposition. Other ambient pressure examples include glow discharge, inductively-coupled, and recombining plasmas. The glow discharge is characterized by low velocity movement of gas of a few meters/second. It features both thermal and chemical non-equilibrium. An inductively-coupled plasma has low to moderate gas movement. It features local thermal equilibria. The recombining nitrogen or air plasmas have high gas velocities of approximately 1 km/sec and feature chemical equilibria. Additional examples of classes of plasmas are determined by their ionization methods such as microwave resonance and electrical discharge.
When plasmas are applied to high volume production processes outside a laboratory, additional manufacturability and automation considerations arise such as speed of operation, compatibility with substrates, and contamination.
In many applications, the plasma treatments occur quickly, typically on the order of nanoseconds to a few minutes, which effectively preclude batch vacuum techniques such as physical vapor deposition.
The high temperature plasmas may thermally combust or thermally shock substrates, especially ones with low thermal conductivity as well as low melting or combustion points.
In addition, some surfaces are imperfect, such as those having dust, organic body oils, and debris from shipment and handling.
In light of the foregoing, what is needed is a method that improves accuracy of manufacturing, productivity, levels of automation, reliability, and/or manufacturability while decreasing harmful side effects, quantity of materials used, and/or waste of energy and materials for a high volume production process for preparing a surface for joining two dissimilar materials or to receive CASE compounds.